This invention relates to a method and apparatus for capturing solar energy and utilizing such solar energy to initiate and sustain endothermic chemical reactions. Such chemical reactions can transduce the solar energy into chemical energy and thereby store the energy until it is required such as by producing a chemical fuel. The method and apparatus also relate to converting solar energy into an easily handleable and storable form of energy which can be recovered when needed rather than utilized only when the sun is shining. Primarily, the method and apparatus concern the carbothermic reduction of metal oxides using solar energy to form a metal carbide which metal carbide can subsequently be processed into fuel or other useful chemical products.
In the process of converting energy into mechanical and electrical power, many forms of energy converters have been utilized. The most widely used converters are gasoline and diesel engines, jet engines, steam turbine engines and gas turbine engines. All of these engines make use of the conversion of a fossil fuel into kinetic energy which is then converted directly to mechanical power. These energy converters are dependent upon fossil fuels or refined fossil fuels, which fossil fuels are becoming ever increasingly less available and more costly. Such fossil fuels also require tremendous capital investment for recovery, refining and distribution.
Tremendous amounts of solar energy, however, are striking the earth's surface every day. Solar insolation has been measured to be about 1 kw/m.sup.2 (or about 0.1 w/cm.sup.2), Eldon C. Boes, et al., "Distribution of Direct and Total Solar Radiation Availabilities for the U.S.A.," Sandia Laboratories Report, SAND 76-0411. Such insolation can provide 20,720 megawatt hours of energy for an eight-hour day on a square mile of the earth's surface. The majority of such solar energy is not being converted to useful energy forms for man's use. Some methods have been developed which make use of the incident solar energy striking the earth's surface. Conventional methods for the utilization of solar energy include methods for the auxiliary heating of dwellings, office buildings and water. Other methods of using solar energy relate to direct use of solar energy for heating steam boilers to provide steam to turn turbines to perform work or to generate electrical energy.
All earthbound solar energy converters are limited generally to a period of up to about 10 to 12 hours of effective operation a day. Such a period is created due to the limited availability of useful sunlight. Therefore, such solar energy converters, which utilize solar energy to provide steam, are operable only periodically and generally must be shut down during periods when the sun is not shining or a secondary means of generating steam during such periods must be provided.
U.S. Pat. No. 277,884 to Clark is directed to reducing refractory metallic ores such as the oxides and chlorides of aluminum, magnesium, calcium and platinum, by exposing such oxides with a reagent such as carbon, to the concentrated rays of the sun. The product of the reduction reaction is the corresponding metal. There is no teaching or suggestion in Clark of carrying out a carbothermic reduction of a metal oxide using solar energy under conditions to produce metal carbides.
U.S. Pat. No. 4,147,534 to Hori discloses the production of calcium and magnesium metal via carbothermic reduction of their oxides and rapid thermal quenching. This is a gas phase equilibrium process for the production of Ca and Mg metal.
U.S. Pat. No. 2,829,961 to Miller discloses a process for producing aluminum metal by reacting Al.sub.4 O.sub.4 C with Al.sub.4 C.sub.3. Miller does not initiate or maintain the endothermic reaction with solar heat, nor does the patent teach the production of aluminum carbides.
British Pat. No. 951,416 discloses the production of metal carbides by reaction of metal oxides with, for example, carbon in a molten menstruum of metallic sodium or potassium.
U.S. Pat. No. 4,049,425 to Middelhoek, et al discloses a process for producing aluminum alloys via carbothermic reduction in the presence of iron, cobalt or nickel at a temperature between 1,000.degree. C. and 1950.degree. C. at subatmospheric pressure.
U.S. Pat. No. 3,101,308 discloses the use of the hierarc principle to transfer energy to a reacting mixture such as, for example, an oxide ore and carbon in order to produce either the metal or a metal carbide. This patent does not disclose use of solar energy to bring about the carbothermic reduction of a metal oxide.